While pre-clinical data demonstrate that combining RPL554 with other bronchodilators produces additional bronchodilation [9, 10], this concept has not been investigated in COPD clinical trials. The future use of RPL554 in clinical practice is likely to be in conjunction with other bronchodilators. We report two phase II clinical trials in COPD patients investigating the bronchodilator effects of RPL554 combined with other bronchodilators. In one study, RPL554 was combined with short-acting bronchodilators; in another study, RPL554 was combined with the long-acting muscarinic antagonist (LAMA) tiotropium.

Methods

Subjects

Both studies were performed at the Medicines Evaluation Unit, Manchester, UK (www.clinicaltrials.gov identifiers NCT02542254 and NCT03028142). Inclusion and exclusion criteria are listed in full in the supplementary material. For both studies, patients with a diagnosis of COPD and a post-bronchodilator forced expiratory volume in 1 s (FEV1) 40–80% predicted were recruited, and COPD patients with significant cardiovascular disease including angina or recent myocardial infarction were excluded. For study 1, FEV1 reversibility >150 mL after inhalation of salbutamol (200 µg) and ipratropium (40 µg) together was required. For study 2, FEV1 reversibility >150 mL after inhalation of salbutamol (400 µg) was required. One patient participated in both studies. Ethical approval was obtained and participants provided written informed consent before screening.

Study design

Study 1 was a randomised, double-blind, placebo-controlled, double-dummy, complete-block six-way crossover study to investigate combination treatment with nebulised RPL554 (6 mg) and salbutamol (200 µg) or ipratropium (40 µg) compared with salbutamol or ipratropium alone (figure 1a). The salbutamol and ipratropium doses are those approved for COPD patients. Long-acting bronchodilator treatment was withdrawn at screening. There were six treatment visits separated by washout periods of 3–14 days. The pre-dose FEV1 at treatment visits was required to be within ±15% of the value at the first treatment visit. On each treatment visit, patients received a single dose (two puffs) from a blinded pressurised metered dose inhaler (pMDI) of salbutamol (200 µg) or matched placebo followed, within 1 min, by a single dose (two puffs) from a second blinded pMDI of ipratropium (40 µg) or matched placebo. This was followed immediately (within 2 min) by a single double-blind dose of either RPL554 (6 mg) or placebo. Spirometry was performed pre-dose and at various times up to 12 h post-dose. Whole-body plethysmography was performed pre-dose and up to 4 h post-dose to obtain measurements of functional residual capacity (FRC), residual volume (RV), total lung capacity and specific airway conductance (sGaw).

Tiotropium was administered open label, while RPL554 or placebo was administered double blind. Spirometry was performed on days 1 and 3 at pre-dose and at various times up to 12 h post-dose, and on day 2 at pre-dose and up to 4 h post-dose. Whole-body plethysmography was performed at pre-dose on day 1 and at pre-dose and 1.25 h post-dose on day 2.

For both studies, patients using inhaled corticosteroids were allowed to continue this treatment during the study. Patients were allowed to use short-acting bronchodilators throughout, but these were withheld for at least 8 h prior to spirometry. RPL554 manufacture and administration using a PARI LC Sprint (PARI, West Byfleet, UK) jet nebuliser is described in the supplementary material. The RPL554 doses were selected based on the results of a preliminary study [11]. Spirometry assessments were performed in accordance with guidelines with three technically acceptable measurements recorded [12]; predicted values were calculated using European Community for Coal and Steel reference equations [13].

Statistical analysis

Sample size calculations are given in the supplementary material. The study 1 primary end-points were change from baseline in peak and average FEV1 over 8 h comparing RPL554+salbutamol versus salbutamol and RPL554+ipratropium versus ipratropium. The study 2 primary end-points were change from baseline (pre-dose day 1) in peak and average FEV1 over 12 h on day 3 comparing RPL554 versus placebo. For both studies, the secondary end-points included onset of action (defined as time to reach 10% increase in FEV1 from baseline), forced vital capacity (FVC), body plethysmography measurements (FRC, RV and sGaw) and safety. ANCOVA models were used as described in the supplementary material.

Results

For both studies, flow diagrams showing the number of patients screened, reasons for screen failure and withdrawals are given in the supplementary material.

Study 1

Table 1 lists the characteristics of the 36 enrolled COPD patients; the mean post-bronchodilator FEV1 was 58.3% predicted with 17.4% reversibility. Six patients did not complete the study: two patients were withdrawn due to chest infections, while four patients failed to meet the criteria for pre-dose FEV1 variability and were withdrawn.

The median time of onset of action (≥10% increase from baseline) for RPL554 was 14.6 min, while for ipratropium bromide and salbutamol this was 18.4 and 6.0 min, respectively. RPL554 administered in combination with either salbutamol or ipratropium bromide reduced the median time of onset to 3.6 min (p=0.009 versus salbutamol alone) and 4.8 min (p<0.0001 versus ipratropium bromide alone), respectively.

Analysis of peak FVC and average FVC(0–8 h) showed greater effects of RPL554 combined with another bronchodilator compared with a bronchodilator alone (analysis shown in supplementary tables S1 and S2).

Study 2

Table 1 lists the characteristics of the 30 enrolled COPD patients; the mean post-bronchodilator FEV1 was 60.1% predicted with 19.5% reversibility. Four patients did not complete the study: two patients were withdrawn because of worsening COPD symptoms, one patient withdrew with pneumonia and one patient withdrew consent.

FEV1

The FEV1 change from baseline (pre-dose on day 1) over 12 h on day 3 is shown in figure 4a. The peak FEV1 changes from baseline for tiotropium combined with placebo or RPL554 1.5 or 6 mg were 373, 477 and 500 mL, respectively (figure 4b). The effects of tiotropium+RPL554 1.5 and 6 mg were significantly greater than tiotropium+placebo (p=0.002 and p<0.0001, respectively). The average FEV1(0–12 h) increase on day 3 was greater with tiotropium+RPL554 6 mg (331 mL) compared with tiotropium+placebo (266 mL; p=0.0009) (figure 4c). There was no difference for tiotropium+RPL554 1.5 mg (317 mL) versus tiotropium+placebo (p=0.09).

On day 1, there were significantly greater FEV1 improvements with tiotropium+RPL554 6 mg compared with tiotropium+placebo, while tiotropium+RPL554 1.5 mg was not significantly different to tiotropium+placebo; these results are shown in the supplementary material. Notably, for peak FEV1 the mean difference between tiotropium+RPL554 6 mg and tiotropium+placebo was 95 mL (p=0.0039). The median time of onset of action on day 1 for tiotropium+RPL554 1.5 and 6 mg was 4.2 and 4.6 min, respectively, compared with 37.6 min for tiotropium+placebo (p<0.0001 for comparisons of RPL554 versus placebo).

Analysis of peak FVC and average FVC(0–12 h) showed a greater effect of RPL554 6 mg compared with placebo (shown in the supplementary material).

Safety

Tiotropium+RPL554 was well tolerated with a similar rate of adverse events compared with tiotropium+placebo (table 4). Withdrawals due to COPD worsening occurred during washout periods and were not attributed to RPL554.

Discussion

We show that RPL554 combined with short-acting bronchodilators or tiotropium caused additional improvements in FEV1 and hyperinflation in reversible COPD patients. In study 1, a single dose of RPL554 6 mg in addition to salbutamol or ipratropium caused significantly greater peak FEV1 improvements compared with either short-acting bronchodilator alone. In study 2, additional improvements in peak, trough and average (0–12 h) FEV1 were observed when RPL554 6 mg was administered with tiotropium for 3 days.

Study 1 was designed to test the mechanistic hypothesis that RPL554 could provide additional bronchodilation in combination with either a β2-agonist or a muscarinic antagonist. This can be regarded as a “proof-of-pharmacology” study to investigate effects caused by different mechanisms of action alone or combined. This study was focused on peak FEV1, and showed similar effects of RPL554, salbutamol and ipratropium administered alone, suggesting that RPL554 causes clinically relevant bronchodilation. The additional effects of RPL554 when combined with short-acting bronchodilators provided mechanistic insights that PDE3/4 inhibition, which increases cAMP levels [7], can cause additional effects when combined with a β2-agonist, which also acts through regulation of cAMP levels [10], or a muscarinic antagonist. Study 1 therefore provided mechanistic support to investigate RPL554 further in combination with long-acting bronchodilator treatment.

Tiotropium was chosen for study 2 as it is a commonly used long-acting bronchodilator. On day 3, the magnitude of additional bronchodilation caused by RPL554 was 116 mL at trough (pre-dose), suggesting that twice-daily RPL554 dosing provides sustained additional bronchodilation persisting for 12 h post-dose. RPL554 6 mg had a greater effect on FEV1 parameters than the 1.5 mg dose and appears to be a suitable twice-daily dose for further investigation. Although study 2 demonstrated an additional effect of RPL554 when administered with a LAMA, it would also be relevant to investigate the effects of RPL554 administered with a long-acting β2-adrenergic agonist (LABA) or a LAMA/LABA combination.

Hyperinflation and gas trapping are major causes of the sensation of dyspnoea, and improvements in lung volumes can improve dyspnoea and exercise performance [14]. RV, a measurement of gas trapping, was reduced by RPL554 in both studies, suggesting a possible effect of RPL554 on small airway function. The onset of bronchodilator action was also faster in both studies when RPL554 was used in combination. A faster onset of bronchodilation may be important to some patients in terms of providing symptom relief.

Pre-clinical studies using human isolated bronchial smooth muscle preparations have demonstrated that RPL554 added to other bronchodilators caused additional bronchodilation, with some evidence of synergistic effects when combined with a muscarinic antagonist [9, 10, 15]. In our clinical trials, additional bronchodilation was observed when using RPL554 in combination with other bronchodilators. While the RPL554 bronchodilator effects are likely to be mainly attributable to PDE3 inhibition, pre-clinical studies have suggested that PDE4 inhibition relaxes inherent tone in isolated human airway tissue [16, 17].

Roflumilast is an orally administered PDE4 inhibitor that reduces exacerbation rates, but the frequency of side-effects, including nausea, weight loss and gastrointestinal disturbance, limits its use in clinical practice [18, 19]. RPL554 was well tolerated in these short-term studies. Clinical trials with a longer duration and larger sample size are needed for proper safety evaluation. RPL554 has the potential for fewer side-effects compared with orally administered PDE4 inhibitors due to reduced systemic exposure, although there may also be intrinsic differences in the pharmacological potential of these different molecules to cause side-effects.

The limitations of the studies reported here include: 1) longer studies are needed to evaluate effects on key clinical end-points, including symptoms and exacerbations, and to properly evaluate safety; 2) the COPD patients included had evidence of reversibility (>150 mL) at screening and the effects of RPL554 in broader population groups need to be studied; 3) the effects of RPL554 in addition to combination treatments that are commonly used in clinical practice remain to be studied, such as LAMA/LABA or triple (inhaled corticosteroid+LABA+LAMA) combinations; and 4) while the anti-inflammatory effects of RPL554 have previously been demonstrated in the LPS challenge model in healthy volunteers [2], further studies of anti-inflammatory effects in COPD patients would be informative.

In conclusion, RPL554 provided additional bronchodilation, reduced gas trapping, improved airway conductance and showed a more rapid onset of action when administered in combination with either a β2-agonist or muscarinic antagonist. These short-term bronchodilator studies provide support to further study RPL554 in longer-term COPD studies focused on other end-points, including symptoms and exacerbations.

Supplementary material

Supplementary Material

Please note: supplementary material is not edited by the Editorial Office, and is uploaded as it has been supplied by the author.

Footnotes

These studies are registered at www.clinicaltrials.gov with identifier numbers NCT02542254 and NCT03028142. This article contains considerable details of the group-level data. The protocol, statistical analysis plan and patient-level data can be accessed by contacting Verona Pharma plc.

Efficacy and safety of RPL554, a dual PDE3 and PDE4 inhibitor, in healthy volunteers and in patients with asthma or chronic obstructive pulmonary disease: findings from four clinical trials. Lancet Respir Med2013; 1: 714–727.